Metal-free photocatalytic reduction of CO2 on a covalent organic framework-based heterostructure

Photocatalytic reduction of CO2 with H2O is thought as an environment friendly approach for sustainable development. It is highly desirable but remains challenging to develop photocatalyst with metal-free site for CO2 reduction. Here, we fabricated a heterostructure by integrating azine-based COF with ZnIn2S4, where the azine unit in COF acts as metal-free sites for CO2 adsorption and reduction. The as-formed interfused heterointerface in the heterostructure ensures the effective electron transfer from ZnIn2S4 across the interface to the COF, resulting in a spatial separation of redox sites for CO2 reduction and water oxidation. The hybrid catalyst exhibits remarkably enhanced photocatalytic activity for CO2 reduction to CO, which is 8 and 6 times than the COF and ZnIn2S4, respectively, and is even comparable with some metal-catalyzed CO2 reduction systems. This study provides a new paradigm to mimic natural photosynthesis by using metal-free site for CO2 reduction.